Terminations of optical fibres in which the end of an optical fibre is mounted in a sleeve member are frequently used, for example, in optical fibre connectors. Optical fibre connectors are understood herein to include connectors for connecting the ends of a pair of optical fibres, as well as connectors which serve to connect an end of an optical fibre to another optical component, e.g. a laser light source or a detector. In optical fibre connectors correct optical alignment of the two fibre cores, or of the fibre core and the beam axis of the optical component, is an essential requirement if undue attenuation and degradation of optical transmission in the connector is to be avoided. Both the alignment of the optical fibre core with another fibre core and the alignment of an optical fibre core with other optical components will be referred to hereinafter for the sake of brevity as fibre alignments and related terms are to be understood accordingly.
In principle, the most convenient way of ensuring correct fibre alignment could be provided by securing the fibre end in a cylindrical sleeve, whose outer cylinder surface is concentric with the core of the fibre, and transferring the alignment function to the outer cylinder surface. In practice, however, serious difficulties present themselves, and these difficulties are especially acute in the case of monomode fibres in which the core is only a few micrometers in diameter and where, consequently misalignment of only a micrometer or two can cause serious transmission losses. A variety of methods have been proposed in the past for aligning the fibre core with the axis of the cylindrical sleeve.
One approach is to machine a sleeve to its final external dimensions and subsequently insert the fibre into an axially extending through-bore of the sleeve. Thereafter the fibre is aligned with the cylinder axis and is secure in the aligned position by means of a hard setting, preferably adhesive, compound such as epoxy-resin or the like.
Another approach is intended to overcome one of the major problems with the method just referred to, which is decentering of the fibre due to non-uniform shrinkage of the compound during setting. It involves inserting and setting the fibre end approximately at the centre of the ferrule and machining the outside of the ferrule, after the compound has set, to be concentric with the fibre by the method disclosed in an article entitled "New Coupling Techniques for Single Mode-Optical Fibre Transmission System" by G. Khoe, published by Optical Communications Conferences, 5th European Conference on Optical Communications, 2nd International Conference on Integrated Optics and Optical Fibre Communications, Amsterdam Sept. 17-19, 1979 pp 6.1-1 to 6.1-4.